Possible bug at intersections

Hi,

There might another issue with the way DFNTrans checks for intersections, which makes particles skip them in some rare cases.

The bug happens when a particle is very close to an intersection, but is in a cell that only has one node in contact with it. The code then defines three variables:

• int1: Node that belongs to that cell and is in contact with the intersection.
• int2: Neighbor node of int1 in contact with the intersection.
• int3: If it exists, second neighbor node in contact with the intersection.

DFNTrans then checks a segment-segment intersection between the particle's trajectory and segment int1<->int2. However, as seen in the figure below, this might not detect the particle crossing the intersection. A possible fix would be to check if int3 exists and, if so, check for an intersection between the particle's trajectory and segment int2<->int3.

Regards,
Jordi

Locate the DFNTrans intersection-checking entry point and trace how int1, int2, and optional int3 are selected. Reproduce the near-intersection case shown in the issue and verify that a particle crossing the intersection is detected when the second segment is needed.